Every day, stores are the victims of shoplifting or "shrinkage", and as a result they suffer loss of earning by amounts that are considerable. The fight against this scourge has led to the development of ever more sophisticated protection systems.
The technological background of the invention can be illustrated by document FR-A-2 605 747 which describes a method consisting in permanently integrating a flat resonant circuit in an object, which circuit operates within a gate that broadcasts a radiofrequency electromagnetic wave, by document FR-A-2 358 713 which describes an antitheft marker of ferromagnetic material fixed on the object that is to be protected, and by document WO-A-85 02285 which describes an alarm system using a tape comprising two superposed strips that are sandwiched between a face of the object and a protective label.
Reference can also be made to document EP-A-0 698 561 and EP-A-0 698 562 describing packaging of heat-shrink plastics material fitted with a metal filament constituting an antenna for an electronic surveillance system operating on a magnetic detection principle, said filament being organized on the inside wall of the packaging in the first document or being integrated in a tear strip in the second document. The techniques described in those documents are advantageous, but they can sometimes be difficult to implement with objects or portions of objects having a section of small size (for example, the temple of a pair of eyeglasses, the clip of a pen).
There also exists an antitheft system using a tie surrounding a portion of the object concerned. Thus, document EP-A-0 615 041 describes a reusable antitheft device for eyeglasses, comprising a tie that is reinforced by two steel cables associated with a fastening plate provided with locking means that can be released only with the help of a special tool.
Various other antitheft systems are known of the type comprising a rigid box or label fixed to the object concerned by staples or by adhesive. Recently, an advanced technology known as "magnetoacoustic" technology has been developed, whereby the antitheft system is constituted by two adjacent metal wafers (separated by an insulating wall) suitable for being set into vibration at a relatively low, predetermined frequency (e.g. about 60 kHz). The advantage of that type of protection system is that the system can be inhibited and reactivated at will, as often as desired. Usually, such a protection system is placed in a box having one adhesive face, so as to be applied directly against a wall of the object to be protected. As will easily be understood, for objects or portions of objects that are of small section, it becomes difficult or even impossible to fix such a box fitted with a magnetoacoustic system, with this being for purely mechanical reasons.